Useful for e.g. generating a COMBINED_FEATURES list from DISTRO_FEATURES and
MACHINE_FEATURES.
(From OE-Core rev: c5b6f672b88f5f42fe0bd59d28104b8dc9ee9a6e)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>